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Chapter 7 Environmental Trends and the U.S. Transportation System � 155
BOX 7-3: DREDGING OF SEDIMENTS IN PORTS AND HARBORS
In 1992, more than 3 billion tons of cargo moved into and out of U.S. ports. Essential for trade and commerce,
these ports handle 95 percent (by weight) of all U.S. exports and imports. Ports and port activities, however, affect
the nation’s coastal, ocean, and freshwater resources. One environmental issue is dredged sediments. In order to
accommodate large cargo ships, navigation channels must be dredged and siltation removed from the harbor
floor. Although estimates vary widely, one study concluded that about 400 million cubic yards of material are
removed each year to maintain the depth of navigation channels and shipping berths. The current permitting
process results in the special handling of about 5 percent of dredged material classified as contaminated.
Siltation is a common problem because many of our nation’s ports (e.g., New York, New Orleans, Baltimore,
and Portland) were built at the mouth of river systems that deliver silt that settles in port channels, making regular
dredging a necessity. As ship size and speed have increased, so too have the requirements for channel
depth. For example, in the 1970s, a depth of 35 feet was considered adequate to handle most maritime trade.
Today, container ships require channel depths of 45 to 50 feet; bulk carriers may require water depths of 60
to 65 feet. For all ports, particularly those with tributary river systems, maintaining channel depth provides a
challenge.
Uncontaminated dredged material can be used beneficially for beach nourishment, wetland creation, and as
caps for landfills, or it can be dumped in certain disposal sites in open waters. Contaminated material, on the
other hand, may have to be treated to reduce its toxicity and managed in special ways, increasing the costs of
navigational dredging. Contaminates include heavy metals and other pollutants, such as dioxins and polychlorinated
biphenyl, that are or have historically been discharged into water and air. Contributing sources are industrial
facilities within ports and upstream, and nonpoint sources such as transportation and agriculture. For
example, bottom sediments in many harbors and rivers of the Great Lakes ecosystem have been found to contain
bioaccumulated toxic substances from past industrial discharges. Contaminates reduce or injure fish and
wildlife populations. Improper disposal of contaminated material can present costly environmental and human
health risks.
Dredge material management is a contentious issue. In some instances, the presence of contaminated sediment
has delayed dredging, thereby affecting waterborne commerce. 1 Uncertainties exist about how best to determine
the extent of contamination in sediments, and there is debate about appropriate management options.
Indiscriminate dumping in the ocean was once a common way to dispose of sediment but is no longer permitted.
Current alternatives include upland disposal and disposal in confined areas within ports and harbors (such as
underwater in covered pits or by constructing islands). Highly contaminated materials may require special remediation
to remove or treat the contaminants before disposal. A National Research Council study, expected to be
issued in late 1996, is examining best management practices and technologies and other issues relevant to contaminated
sediments.
National and state regulations have been developed to address dredging and appropriate sediment management
to maintain the environmental integrity of the nation’s coastal resources. Under statutes, such as the Clean
Water Act (CWA) and the Marine Protection, Research, and Sanctuaries Act (MPRSA), a number of agencies have
been given authority for various stages of the dredging and disposal process. Under the MPRSA, for instance, the
U.S. Army Corps of Engineers issues permits covering dredged materials disposed in most coastal waters and the
open ocean; the Environmental Protection Agency has review authority, designates specific ocean disposal sites,
and established the environmental impact criteria used by the Corps of Engineers in the permit review process.
1 Council on Environmental Quality, Office of the President, Twenty-Fourth Annual Report (Washington, DC: U.S. Government Printing Office, 1993).
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